FISH OIL, NUTS, OMEGA-3 FATTY ACIDS AND THE HEART

DISCLAIMER: THIS PAGE CONTAINS A GENERAL EDUCATIONAL DISCUSSION ON THE ABOVE TOPIC. IT IS NOT HEALTH ADVICE AND SHOULD NOT BE CONSTRUED AS SUCH. YOU SHOULD NEVER RELY UPON THE INFORMATION GIVEN HERE. YOUR PARTICULAR CIRCUMSTANCES MAY WELL REQUIRE AN ENTIRELY DIFFERENT APPROACH. YOU SHOULD NOT MAKE ANY CHANGES IN YOUR MEDICATIONS, DIET, ACTIVITY, LIFESTYLE, ETC. WITHOUT FIRST CONSULTING A LICENSED PHYSICIAN IN YOUR AREA.

TABLE OF CONTENTS:

Populations who eat a lot of fish tend to have a low incidence of heart disease. It has been suggested that the oils in fish are responsible for this beneficial health effect.

Fish oil contains a special type of polyunsaturated fat called omega-3 fatty acids. They are also called n-3 PUFAs. There are two types of fat in fish oil: eicoapentanoic acid (EPA) and docosahexanoic acid (DHA).

Different types of fish contain different amounts of these fats. Various information sources differ on how much omega-3 fatty acids each type of fish has. In general, the highest amounts of these fatty acids are found in mackerel, salmon, trout, herring, and tuna. See the tables at the bottom of this page for more details. Fried fish and fish sandwiches seem to be less helpful for the heart. Frying may inactivate the omega-3 fats in fish. So it is best to prepare the fish by broiling or baking.

A similarly beneficial n-3 PUFA fat known as a -Linolenic acid is found in flaxseed, flaxseed oil, canola oil, soy, soybean oil and nuts (especially English Walnuts), dairy products, broccoli, green leafy vegetables and beans (especially pinto beans). You should avoid hydrogenated soybean oil however as the hydrogenation process produces undesirable trans fatty acids.

Omega 3 fatty acids have many beneficial effects. They lower triglyercide levels and have a minimal effect on LDL (bad) cholesterol. Unfortunately, they contain fat calories. They have a blood thinning effect which can help protect against heart disease but may increase bleeding risks. They minimally lower blood pressure. Omega-3 fatty acids may also exert their beneficial effect biochemically in part by altering the balance between different types of prostaglandin molecules produced by many tissues in the body. Fish oils have antiinflammatory effects. They help blood vessels dilate and inhibit the development of atherosclerosis.

However, it appears that the main way they help is by stabilizing the electrical conduction system of the heart. This helps prevent against rapidly fatal irregularities in the heart rythm which often occur in patients with atherosclerosis. Studies have shown that these fats do lower the risk of dying suddenly from heart disease. This benefit occurs in people with established heart disease and in people without any evidence of heart disease.

Unfortunately, as in so many medical studies, controversy exists. Some studies have suggested that some harm may be caused by fish oils.

Whether people should take omega 3 fatty acids supplements or just eat more of the aforementioned food products has not been determined. One study showed that heart attack survivors who ate fatty fish twice a week were less likely to die than those who didn't. Another study demonstrated a similar benefit in heart attack surviors who ingested just one fish oil capsule a day. (The capsule in that study contained 850-882 mg. of eicoapentanoic acid (EPA) and docosahexanoic acid (DHA) as ethyl esters in a ration EPA:DHA of 1:2. A typical fish oil capsule sold in stores contains 1000 mg of fish oil of which 180 mg is EPA and 120 mg is DHA. The other 700 mg are other oils not known to be of benefit. Other commercially available products may contain greater or lesser amounts of EPA and DHA in the 1000 mg capsule so read the lable closely. A detailed description of these fish oil supplements is available at http://www.consumerlab.com/results/omega3.asp)

Each brand of fish oil supplement differs in how much EPA and DHA are in each capsule. The U.S. Pharmacopeia (http://www.usp.org) has tested some of te supplements to confirm they contain their labeled content and do not contain mercury or other toxins.

Studies of people without heart disease also showed a protective effect from eating fish or fish oil supplements. The more a person eats, the greater the benefit. Most authorities recommend eating fish twice a week.

The American Heart Association recommendation for the average person is 0.5 grams per day of EPA + DHA and 1.0 gram per day of a -Linolenic acid. The American Heart Association recommendation for patients with heart disease is 1.0 gram per day of EPA + DHA. Some authorities recommend as much as three grams per day. See the tables at the bottom of this page for the fish oil content for each type of fish and the content for vegetable oils, nuts and seed.

As mentioned above, nuts also contain omega-3 fatty acids. Studies have shown that eating nore nuts reduces risk of suddenly dying from heart disease. Nuts are a component of the Mediterranean Diet.

For the scientifically inclined, omega-3 polyunsaturated fatty acids contain a double bond at the third carbon position whereas the more common polyunsaturated fatty acids found in food (the omega-6 fatty acids or n-6 PUFAs) contain the first double bond at the sixth carbon position.

One problem with fish is mercury contamination. The fish with the highest mercury content are generally those with the longest lives and those at the top of the food chain. This includes salt water fish such as shark, swordfish, mackeral and tuna; fresh water fish such as pike and bass and bottom feeders such as crab. More informations can be obtained at the following web site : http://www.epa.gov/waterscience/fish/states.htm and at the table further down on this page.

Mercury is particularly dangerous to the fetus and children. Thus, women who are pregnant, women who may become pregnant, women who are breast feeding and young children are advised to avoid the fish that have the highest mercury content (tilefish, swordfish, mackeral and shark). Seafood that is low in mercury includes salmon, canned light tuna, pollock, catfish and shrimp.

Symptoms of mercury poisoning include tremors, difficulty concentrating, numbness, tingling and visual difficulties. However, not everybody with a high mercury levels will necessarily have any symptoms. Mercury levels can be check with a simple and inexpensive blood test. Mercury from fish is excreted into the feces and not into the urine. If one has an elevated level of mercury in the blood and the urine, the source of the mercury is not from fish and more likely from and inorganic source such as a job exposure.

Low level mercury elevations are treated by reducing fish intake. Chelation therapy (penicillamine, dimercaprol or succimer) can be considered for high levels but these treatments are most commonly employed for inorganic (e.g., job-related) exposures, not for fish ingestion.

Other toxins found in fish are carcinogens (cancer caussing substances) such as dioxin and polychlorinated biphenyls (PCBs). In addition to being carcinogens they can also affect the central nervous system. They were used in paints, flame retardants, pesticides and inks. They have now been banned from use by the United States government. Unfortunately, they are still found in polluted waters and the fish that live in those polluted waters. They can also be found in other food sources (meat, poultry and dairy) but fish are the main source.

PCBs are most commonly found in freshwater fish that live in inland lakes such as bluefish, lake trout and smelt. The contamination of fish varies in each region of the United States. More information about a specific region can be obtained at the following web site : http://www.epa.gov/waterscience/fish/states.htm.

Unfortunately, farmed (but not wild) salmon is high in PCBs. This is unfortunate because salmon is otherwise an excellent source of fish oil and quite low in mercury. The reason for the high levels in farmed salmon appears to be that they are fed fish that are high in PCBs. Supposedly, the salmon farming industry is changing this practice so this will hopefully be less of a problem in the future.

Lean ocean fish such as cod, flounder and haddock tend to be the lowest in PCBs. Fatty fish caught locally tend to have high levels as they come from polluted water and the PCBs primarily accumulate in fat. If one eats these local fish, it has been advised to remove the fatty areas such as the belly, back and dark side meat; remove or puncture the skin and cook the fish on a rack to allow the fat to drain. Frying fish should be avoided. The rub here is tha the helpful fish oils are in the fat, so removing the fat to avoid PCBs also reduces the benefit of eating the fish.

Many fish do not seem to provide any health hazard. These include flounder, farmed rainbow trout, sole, anchovies, and farmed clams and shrimp. Other fish are felt to be safe in moderation, such as once a week. These include cod, famed catfish, mahi mahi, wild salmon, tilapia, and canned chunk tuna.

Fish oils can also be obtained from nonfish sources. As noted above, one can cook with or eat flaxseed, flaxseed oil, canola oil, soy, soybean oil and nuts (especially English Walnuts), dairy products, broccoli, green leafy vegetables and beans (especially pinto beans).

One can also buy fish oil supplements. The amount of mercury in fish oil supplements is less than that found in fish and authorities do not consider their mercury content to be a problem. Fish oil supplements may also contain carcinogens. This is particularly true for products marketed as cod liver oil. Lower amounts are present in products marketed as fish oil supplements. Most authorities feel that the amount of carcinogens in fish oil supplements is insignificant in that they do not contribute significantly to the total carcinogen intake in our diet

Three tables follow. One lists the amounts of fish oil (EPA + DHA) in most types of fish. The second lists the a -Linolenic acid content of vegetable oils, nuts and seed. The third lists the mercury content of various types of fish.

Amounts of EPA+DHA in Fish and Fish Oils and the Amount of Fish Consumption Required to Provide 1 g of EPA+DHA per Day :

Mercury Levels in Seafood Species

The following tables provide the mean and range of mercury levels in a variety of fish and shellfish

**Fish and Shellfish With Highest Levels of Mercury**
SPECIES	MERCURY CONCENTRATION (PPM)				NO. OF SAMPLES	SOURCE OF DATA
SPECIES	MEAN	MEDIAN	MIN	MAX	NO. OF SAMPLES	SOURCE OF DATA
MACKEREL KING	0.73	NA	0.23	1.67	213	GULF OF MEXICO REPORT 2000
SHARK	0.99	0.83	ND	4.54	351	FDA SURVEY 1990-02
SWORDFISH	0.97	0.86	0.10	3.22	605	FDA SURVEY 1990-02
TILEFISH (Gulf of Mexico)	1.45	NA	0.65	3.73	60	NMFS REPORT 1978

**Fish and Shellfish With Lower Levels of Mercury**
SPECIES	MERCURY CONCENTRATION (PPM)				NO. OF SAMPLES	SOURCE OF DATA
SPECIES	MEAN	MEDIAN	MIN	MAX	NO. OF SAMPLES	SOURCE OF DATA
ANCHOVIES	0.04	NA	ND	0.34	40	NMFS REPORT 1978
BUTTERFISH	0.06	NA	ND	0.36	89	NMFS REPORT 1978
CATFISH	0.05	ND	ND	0.31	22	FDA SURVEY 1990-02
CLAMS	ND	ND	ND	ND	6	FDA SURVEY 1990-02
COD	0.11	0.10	ND	0.42	20	FDA SURVEY 1990-03
CRAB ³	0.06	ND	ND	0.61	59	FDA SURVEY 1990-02
CRAWFISH	0.03	0.03	ND	0.05	21	FDA SURVEY 2002-03
CROAKER (Atlantic)	0.05	0.05	0.01	0.10	21	FDA SURVEY 1990-03
FLATFISH ²	0.05	0.04	ND	0.18	22	FDA SURVEY 1990-02
HADDOCK	0.03	0.04	ND	0.04	4	FDA SURVEY 1990-02
HAKE	0.01	ND	ND	0.05	9	FDA SURVEY 1990-02
HERRING	0.04	NA	ND	0.14	38	NMFS REPORT 1978
JACKSMELT	0.11	0.06	0.04	0.50	16	FDA SURVEY 1990-02
LOBSTER (Spiny)	0.09	0.14	ND	0.27	9	FDA SURVEY 1990-02
MACKEREL ATLANTIC (N. Atlantic)	0.05	NA	0.02	0.16	80	NMFS REPORT 1978
MACKEREL CHUB (Pacific)	0.09	NA	0.03	0.19	30	NMFS REPORT 1978
MULLET	0.05	NA	ND	0.13	191	NMFS REPORT 1978
OYSTERS	ND	ND	ND	0.25	34	FDA SURVEY 1990-02
PERCH OCEAN	ND	ND	ND	0.03	6	FDA SURVEY 1990-02
PICKEREL	ND	ND	ND	0.06	4	FDA SURVEY 1990-02
POLLOCK	0.06	ND	ND	0.78	37	FDA SURVEY 1990-02
SALMON (Canned)	ND	ND	ND	ND	23	FDA SURVEY 1990-02
SALMON (Fresh/Frozen)	0.01	ND	ND	0.19	34	FDA SURVEY 1990-02
SARDINE	0.02	0.01	ND	0.04	22	FDA SURVEY 2002-03
SCALLOPS	0.05	NA	ND	0.22	66	NMFS REPORT 1978
SHAD (American)	0.07	NA	ND	0.22	59	NMFS REPORT 1978
SHRIMP	ND	ND	ND	0.05	24	FDA SURVEY 1990-02
SQUID	0.07	NA	ND	0.40	200	NMFS REPORT 1978
TILAPIA	0.01	ND	ND	0.07	9	FDA SURVEY 1990-02
TROUT (Freshwater)	0.03	0.02	ND	0.13	17	FDA SURVEY 2002-03
TUNA (Canned, Light)	0.12	0.08	ND	0.85	131	FDA SURVEY 1990-03
WHITEFISH	0.07	0.05	ND	0.31	25	FDA SURVEY 1990-03
WHITING	ND	ND	ND	ND	2	FDA SURVEY 1990-02

**Mercury Levels of Other Fish and Shellfish**
SPECIES	MERCURY CONCENTRATION (PPM)				NO. OF SAMPLES	SOURCE OF DATA
SPECIES	MEAN	MEDIAN	MIN	MAX	NO. OF SAMPLES	SOURCE OF DATA
BASS (Saltwater)¹	0.27	0.15	0.06	0.96	35	FDA SURVEY 1990-03
BLUEFISH	0.31	0.30	0.14	0.63	22	FDA SURVEY 2002-03
BUFFALOFISH	0.19	0.14	0.05	0.43	4	FDA SURVEY 1990-02
CARP	0.14	0.14	0.01	0.27	2	FDA SURVEY 1990-02
CROAKER WHITE (Pacific)	0.29	0.28	0.18	0.41	15	FDA SURVEY 1990-03
GROUPER	0.55	0.44	0.07	1.21	22	FDA SURVEY 2002-03
HALIBUT	0.26	0.20	ND	1.52	32	FDA SURVEY 1990-02
LOBSTER (Northern/American)	0.31	NA	0.05	1.31	88	NMFS REPORT 1978
MACKEREL SPANISH (Gulf of Mexico)	0.45	NA	0.07	1.56	66	NMFS REPORT 1978
MACKEREL SPANISH (S. Atlantic)	0.18	NA	0.05	0.73	43	NMFS REPORT 1978
MARLIN	0.49	0.39	0.10	0.92	16	FDA SURVEY 1990-02
MONKFISH	0.18	NA	0.02	1.02	81	NMFS REPORT 1978
ORANGE ROUGHY	0.54	0.56	0.30	0.80	26	FDA SURVEY 1990-03
PERCH (Freshwater)	0.14	0.15	ND	0.31	5	FDA SURVEY 1990-02
SABLEFISH	0.22	NA	ND	0.70	102	NMFS REPORT 1978
SCORPIONFISH	0.29	NA	0.02	1.35	78	NMFS REPORT 1978
SHEEPSHEAD	0.13	NA	0.02	0.63	59	NMFS REPORT 1978
SKATE	0.14	NA	0.04	0.36	56	NMFS REPORT 1978
SNAPPER	0.19	0.12	ND	1.37	25	FDA SURVEY 2002-03
TILEFISH (Atlantic)	0.15	0.10	0.06	0.53	17	FDA SURVEY 2002-03
TUNA (Canned, Albacore)	0.35	0.34	ND	0.85	179	FDA SURVEY 1990-03
TUNA (Fresh/Frozen)	0.38	0.30	ND	1.30	131	FDA SURVEY 1990-02
WEAKFISH (Sea Trout)	0.25	0.16	ND	0.74	27	FDA SURVEY 1990-03

Source of data: FDA Surveys 1990-2003
"National Marine Fisheries Service Survey of Trace Elements in the Fishery Resource" Report 1978
"The Occurrence of Mercury in the Fishery Resources of the Gulf of Mexico" Report 2000

Market share calculation based on 2001 National Marine Fisheries Service published landings data
* Mercury was measured as Total Mercury and/or Methylmercury

ND - mercury concentration below the Level of Detection (LOD=0.01ppm)
NA - data not available
¹ Includes: Sea bass/ Striped Bass/ Rockfish
² Includes: Flounder, Plaice, Sole
³ Includes: Blue, King, Snow